Various types of semiconductor devices such as electrically erasable programmable read-only memories (EEPROMs) and ferroelectric random access memories (FeRAMs) are known as semiconductor devices from which data does not disappear even after a power supply is stopped.
Among such semiconductor devices, EEPROMs store data by storing charge in a floating gate, and are widely used in the form of a flash memory. However, when EEPROMs are irradiated with radiation, the charge in the floating gate easily flows to the outside, and thus EEPROMs have low radiation resistance.
On the other hand, FeRAMs store data not by utilizing stored charge but by making the direction of polarization of a ferroelectric film correspond to “0” or “1”. Accordingly, FeRAMs have higher resistance to radiation than the EEPROMs do.
In the medical field, high-energy gamma rays are used for sterilizing medical appliances. Furthermore, devices used in nuclear power plants or outer space are also exposed to radiation having high energy, such as an electron beam or a neutron beam.
By further enhancing the radiation resistance of FeRAMs, products that may be used under such high-energy radiation may be provided, and furthermore, a new market of FeRAMs may be developed.
For example, Japanese Laid-open Patent Publication No. 05-343617 discloses a semiconductor memory device.